EFFICACY OF DIRECT INTRATUMORAL THERAPY WITH TARGETED PROTEIN TOXINS FOR SOLID HUMAN GLIOMAS IN NUDE-MICE

Targeted protein toxins are a new class of reagents with the potential for great tumor selectivity and cytotoxic potency. Two such compounds were studied: 1) Tf-CRM107, a conjugate of human transferrin (Tf) and diphtheria toxin with a point mutation (CRM107); and 2) 454A12-rRA, a conjugate of a monoclonal antibody (454A12) to the human Tf receptor and recombinant ricin A chain (rRA). Both compounds are potent and spe cific in killing human glioblastoma cell lines in vitro. The authors i nvestigated the activity of these reagents administered intratumorally against solid U251 MG human gliomas in vivo. Nude mice with establish ed U251 MG flank tumors (0.5 to 1.0 cm in diameter) were randomly assi gned to be treated with 100-mu l intratumoral injections of Tf-CRM107 (10 mu g) or 454A12-rRA (10 mu g), equimolar doses of CRM107 (4.3 mu g ), 454A12 antibody (7.5 mu g), or rRA(1.5 mu g), or phosphate-buffered saline (PBS) every 2 days for a total of four doses. Tumor volume and animal weight were assessed by a blinded observer before each treatme nt and biweekly for 30 days after initiating therapy. With Tf-CRM107 a dministration, tumor regression of greater than 95% occurred by Day 14 (p < 0.01) and tumors did not recur by Day 30. Treatment with 454A12- rRA caused a 30% decrease in tumor volume by Day 14 (p < 0.01). Treatm ent with equimolar doses of the unconjugated targeted protein toxin co mponents CRM107, 454A12, or rRA caused significant U251 MG tumor growt h inhibition, but the effects were less potent than the antitumor effe cts of the conjugates. This study also characterized the dose-response effect of Tf-CRM107 on tumor growth and tumor weight on Day 30. Nude mice with established U251 MG flank tumors (0.5 to 1.0 cm in diameter) were treated with 100-mu l intratumoral injections of 10, 1.0, or 0.1 mu g of Tf-CRM107 or PBS every 2 days for a total of four doses. Ah t hree doses of Tf-CRM107 significantly inhibited tumor growth by Day 14 (p < 0.01) and at Day 30 (p < 0.05), with a significant dose-response relationship. This study demonstrated in vivo efficacy of the targete d toxins Tf-CRM107 and 454A12-rRA against a human glioma. With intratu moral administration, the effect of Tf-CRM107 was tumor-specific and i n some animals curative. Regional therapy with these potent tumor-spec ific agents using direct intratumoral infusion should limit systemic t oxicity and may be efficacious against brain tumors.